Method for recovery of nitroform from a reaction mixture containing nitric acid and nitroform

ABSTRACT

Nitroform is separated from reaction mixtures containing concentrated nitric acid by adding to the mixture an amount of water sufficient to reduce and subsequently maintain the content of nitric acid present therein below 68 per cent, and then submitting the diluted mixture to distillation whereby nitroform, together with water, is obtained as distillate.  In a preferred embodiment, some of the nitric acid is distilled off from the initial mixture before water is added.  If the distillation is carried out under partial vacuum, the concentration of NHO3 must be maintained below about 66.5 per cent.  In an example, a reaction mixture, obtained by nitration of acetylene, contained nitroform (10.5 per cent), nitric acid (75 per cent) and water (12.5 per cent).  About half of the nitric acid was distilled off through a column under a pressure of 200 mm., giving a residue containing 18 per cent nitroform, 56 per cent nitric acid and 23 per cent water. The contents of the still were diluted with water to make the composition 14.5 per cent nitroform, 46.5 per cent nitric acid and 39 per cent water, and the diluted mixture was distilled using the column at a pressure of 150 mm. to give an aqueous distillate, containing 47 per nitroform, which separated in two phases.  The lower layer was 90 per cent nitroform.

Paten ted Nov. 3, 1953 Swedish company METHOD FOR RECOVERY, OF m'rRoFoRM" FROM A REACTION lVHXTURE CONTAIN- ING NITRIC ACID AND NITROFORM Gustav Allan Wetterholm and Ernst Lennart Nilsson, Gyttorp, Sweden, assignors to Nitroglycerin Aktiebolaget,

Gyttorp, Sweden, a

No Drawing. Application August 25,1952, Serial No. 306,286 Claims priority, application Sweden" August 28, 1951" The present inventionconcernsa method for recovery of nitrofor'm in pure or practically pure state from a reaction 'mixture containing principally concentrated nitric acid and nitroform.

'Nitroform can beproduced according to known methods by introducing acetylene gasinto concentrated nitric acid (Orton and McKee, J. C. S., 1920) under catalysis with mercury salts. In this manner a solution is obtained, which contains approximately"70-' 90% nitric acid, -11% nitroform, the remaining being water, small amounts of oxalic acid,j nitrose etc.

On account of the'great similarity between nitroiorm and nitric acid, the production of the former in pure 'form meets with considerable difficulties. Thus it is not possible to isolate nitro'-' form by direct distillation, as 'a' mixture of nitroform and nitric acid, or nitric acid alone at the beginning, passes over. Precipitation or freezing out methods have? sufjar not found technical application. Extraction'pf the nitroform with liquid nitrogen dioxide, which has also been proposed, is connected withi'considerable difiiculties and has hitherto not been carried out technically. The above mentioned' di'fiiculties are obviated by the present invention. This invention is based The conditions, on which the process according to the invention are based, will be apparent from the following statements. Nitric acid-water has, when pure, a maximal azeotrope at a concentration of 63% by weight of I-INOa and 32% ofwat'er If the relation HNOaZI-IzO in the reaction mixture is richer in nitric acid than that, which corresponds to the composition of the azeotrope, concentrated nitric acid will distill over. If the relation approximately corresponds to the composition of the azeotrope, a mixture of nitric acidwater-nitroformwill distill over. If on the other hand less nitric acid is present than in accordance with this relation, nitroform-water will distill over, free from nitric acid or only containing traces thereof, while the contents of the still will be free or practically free from nitroform.

The reduction in the contents of nitric acid 6 Claims. ((31. 260-4344) .2 in the reaction mixture to the desired concentra'-' tion may be efiected either by direct dilution with water or in such a way, that nitric acid is distilled ofi first and until the azeotropic composition is approximately obtained and the solution then diluted with a small amount of water. This lat ter manner of working is especially advantageous, as will be shown below. I

The nitroform-w'ater mixture obtained by the distillation divides itself during condensation into two layers due to theiactthat nitroform and water are only partially soluble in one another and cannot mix in all proportions. The upper strongly yellow-coloured layer contains 35-45%; nitroformand is free, or nearly free from nitric acid; while the lowerlaye'rcontains 90-95% nitro form, free from or only-with traces-of nitric acid.

The nitroform' thusobtained may by re"- cry'stallisation; for example from carbon? tetrachlcride, be obtained in crystallized condition the form of long-white needles with a-melting point Of 28 C: v if For recovering nitric acid. from-the reaction mixtureit is of specialimportance that a s h'as" been mentioned above, it has' been proved po's ble, by the' use of fractional distillation mpg umns, first to remove from the reaction mixture that part: of the nitric acid, which exceeds'the amount of HNOs' corresponding to the relation of 68% HNO3 to 32% E20, after which there maining solution is diluted'with a suitable amount of water, as previously indicated, whereafter the distillation can take place. i

By nitration ofacetyleii with concentrated tric acida solution was obtained,:which was .fi t' relieved from nitrose; It "then ha'dthe following composition: 10.5% i nitrotorm, 74.8% iI-INO:",T1 0% l HNOi;."1J2%' oxalic acid and 12.5% water. y; coliim'n distillationjfof this soiuuon'undera' priesure of 200 Hg a distillate was obtained coir-I". taining"97i8"%" HN'O, 1.8% t'etr'anitrom'ethan and Q the rest water. The boiling temperature'in'the" still was about C. and that of the departing gases 45-50 C. The composition of the remaining solution in the still was 18.2% nitroform, 56.2% I-lNOg, 0.6% HNOz, 1.6% oxalic acid and the rest water (23.4%). The relation nitric acidwater was here 2.41 as against 2.13 in a constantly-boiling mixture of only nitric acid and water (68:32). This depends on the fact, that it is practically impossible to distill ofi" from the reaction mixture sufiicient concentrated nitric acid to make the nitric acid content of the still correspond exactly with the composition of the azeotrope nitric acid-water. Of the amount of nitroform supplied 95 was found in the still after discontinuation of the distillation, while 50% of the nitric acid had distilled over.

The contents of the still was now i 5] diluted with.

enough water to make the composition: 14.5% columns substantially the excess of nitric acid nitroform, 46.5% HNOs and 39.0% water apart from oxalic acid and traces of nitrous acid. When this solution was distilled in the column a distillate (in two phases) was obtained with a total composition of 47% nitroform, 52.5% water and 0.5% I-lZNOs. The solution remaining in the still contained 68.0% HNOs, 31.8 H2O and,0.2% nitroform.

tory conditions can naturally be improved upon by the use of larger apparatus. The distillation I Example 2 In a nitration experiment a solution was obtained with a composition of 9.2% nitroform, 72.4% HNOs, 5.7% HNOz, 1.1% oxalic acid and the rest water. After addition of 30% water based on the total volume of the solution and simultaneous blowing of air therethrough, a solution was obtained having a content of 7.82% nitroform, 56.2% HNOa, the rest being water, oxalic acid and traces of nitrose.

By distillation of this solution a distillate was obtained containing 51.6% nitroform, 1.0% I-INOs and the rest water, while the composition of the remaining solution in the still amounted to 68.35% HNOs, 0.01% nitroform, the rest water, oxalic acid etc. The recovery of nitroform by the distillation was 95.9% and of HNO3 in the still, 98.8%. During condensation the distillate separated into two layers, an upper one containing 40.5% nitroform, 0.01% HNO3 plus some water, and a lower one containing 90.0% nitroform and 0.0% HNOs.

We claim:

1. A method of recovering nitroform from a reaction mixture containing concentrated nitric acid and nitroform, which comprises reducing the content of nitric acid in the mixture down below the concentration which corresponds to an azeotropic mixture of nitric acid and water, distilling the mixture thus obtained, whereby vapours of practically pure nitroform and water pass over, condensing the vapours, and then recovering the nitroform from the distillate thus obtained.

The recovery of nitroform obtainedby the distillation amounted to 95.5%, and of the nitric acid remaining in the still 98% was recovered. These yields which were obtained under labora-. .j:

4 2. The method according to claim 1, wherein the distillation is carried out in a partial vacu- 3. A method of recovering nitroform from a reaction mixture containing concentrated nitric acid and nitroform, which comprises removing from the mixture by fractional distillation in over the nitric acid content of an azeotropic 'mixture of nitric acid and water, adding an amount of water sufiicient to reduce the content of nitric acid in the mixture below the azeotropic concentration, distilling the mixture thus obtained, whereby vapours of practically pure nitroform and water pass over, condensing the vapours, and then recovering the nitroform from the distillate thus obtained.

' 4. A method of recovering'nitroform from a reaction mixture containing concentrated nitric acid and nitroform, which comprises adding directly to the reaction mixture an amount of water sufiicient to reduce the content of nitric acid present therein below the content of nitric acid in an azeotropic mixture of nitric acid and Water, distilling the mixture thus obtained, whereby vapours of practically pure nitroform and water pass over, condensing the vapours, and then recovering the nitroform from the distillate thus obtained.

5. A process for producing pure nitroform, which comprises reacting acetylene with concentrated nitric acid, removing from the reaction mixture by fractional distillation in columns substantially excess of nitric acid present therein over the nitric acid content of an azeotropic mixture of nitric acid and water, adding an amount of water sufficient to reduce the content of nitric acid in the mixture below the azeotropic concentration thereof, distilling the mixture thus obtained in a partial vacuum, whereby vapours of practically pure nitroform and water pass over, condensing the vapors, and then recovering the nitroform from the distillate thus obtained.

6. The process of claim 5 wherein the distillation is carried out in a partial vacuum amounting to -200 mm. Hg.

GUSTAV ALLAN WET'IERHOLM.

ERNST LENNART NILSSON.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,233,620 Lippincott Mar. 4, 1941 2,465,959 Tindall Mar. 29, 1949 OTHER, REFERENCES 

5. A PROCESS FOR PRODUCING PURE NITROFORM, WHICH COMPRISES REACTING ACETYLENE WITH CONCENTRATED NITRIC ACID, REMOVING FROM THE REACTION MIXTURE BY FRACTIONAL DISTILLATION IN COLUMNS SUBSTANTIALLY EXCESS OF NITRIC ACID PRESENT THEREIN OVER THE NITRIC ACID CONTENT OF AN AZEOTROPIC MIXTURE OF NITRIC ACID AND WATER, ADDING AN AMOUNT OF WATER SUFFICIENT TO REDUCE THE CONTENT OF NITRIC ACID IN THE MIXTURE BELOW THE AZEOTROPIC CONCENTRATION THEREOF, DISTILLING THE MIXTURE THUS OBTAINED IN A PARTIAL VACUUM, WHEREBY VAPOURS OF PRACTICALLY PURE NITROFORM AND WATER PASS OVER, CONDENSING THE VAPORS, AND THEN RECOVERING THE NITROFORM FROM THE DISTILLATE THUS OBTAINED. 